Funding for this research was provided by:
Yunnan Applied Basic Research Projects-Kunming Medical University Union Foundation (2018FE001(-132))
National Natural Science Foundation of China (81703324)
China Scholarship Council (201808535098)
Received: 5 June 2019
Accepted: 12 December 2019
First Online: 23 December 2019
Ethics approval and consent to participate
: This study was approved by the Ethics Review Board of Kunming Medical University. In addition, a written consent was obtained from either the parent or legal guardian. For boarding students, upon the approval of the ethics review board, written consents were obtained from teachers. All participated students aged 16 or above also provided written consents to participate by themselves.
: Not applicable.
: The authors declare that they have no competing interests.